Centrifugal gas separator



Feb. 21, 1939.

c;A l.. PRATT CENTRIFUGAL GAS SEPARA'IOR Filed July l5, 1937 n mwmmmw /Illllrl l PatentelFeb. 21,1939.'

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i i E CENTRIFUGAL GAS SEPABATE George L. Pratt, Atlanta, Ga., assignmto Motor Power, Inc., Atlanta, Ga., a corporation ci? Georgia Application .duly i5, i937, Serial lilo. lbttt iii matins. (CL. Mdm-2i rihis invention relates to gas separators and concerns particularly a device of this character designed for treating exhaust gases ot internal combustion engines to obtain therefrom a supply 5 of gases of improved combustion characteristics suitable for combustion as fuel in such engines. .Exhaust gases discharged by internal combus tion engines comprise a mixture ol ingredients resulting `from the chemical breah down ot tuoi 1o exploded in the engine. Certain ol such. exhaust v ingredients are combustible and under proper conditions may be reutilized in an engine. @ther ingredients are non-combustible and diiute the combustible gases. One of the latter; carbon is dioxide, has adefinite combustion blanlreting eiiect. Mixed exhaust gases in their ordinary state and with normal proportions oi combustible and non-combustible ingredients can not be subjected to combustion and power production in an 2@ engine, and if any substantial quantity thereof is supplied will retard or prevent combustion ot ordinary fresh iuel.

The essential object oi the invention is to provide a device which will produce from the exhaust 2 gases a segregated portion thereof suitable for combustion engine operation and under condi-- tions and for purposes which can not be satisded 4by the gases as produced from the engine.

The combustible ingredients oi the exhaust 3@ gases are llighter than the non-combustible in,-

gredients and the device of the present invention taires advantage ofsuch fact to euect through centrifugal separation a treatment on the basis of the difference in specific gravities, thereby to 35 produce a useful gas supply for engine operation wherein the proportion of combustible ingredi-v ents is increased and the proportion of the non;- combustible and combustion retarding ingredients is reduced.

io Because of the nature of mixed gases-complete segregation by centrifugal action as between the lighter combustible exhaust gases and the heavier non-combustible portion thereof; while desirable, appears impossible under practical operating conditions.' The present invention does not purport to'make any complet-e separation but only f to effect a partial separation such that the portion intended to be used for combustion has an increased proportion of combustibles and a diminished pro-portion of non-combustibles. The utility of the device is premised on the fact that even a small improvement in the relation between combustible and non-combustible v ingredients 55 tremendously improves the combustible character oi the mired erhaust pases tor purposes oi engine operation.

The above and other objects oi the invention and the structure torv attaining the same will ben come evident from the subsequent description ot .d

the main embodiment oi the invention together with several modincations which are .shown in the accompanyins drawing wherein:

Fig. 1 is aview in longitudinal section oi a con struction embodyine the main tentures oi the l@ invention;

Fia. 2' is a cross-sectional view taben on the line t-t or rieure i;

litig. 3 'is a view generally similar to Figure i showinp a modiiication; il Fig. d is a View in lonpitudinal section showina a further niocation oi' the main construction;

. and

Fig. 5 is a longitudinal section or a simplihed further embodiment oi the invention. zo

The essential features oi the invention as shown in Figures i and 2 include a main tubular separator casing iii having at or adjacent one end a gas inlet il. @uch casina will be closed except for outlets tor separated cases hereafter 2o to be reierred to. Extendida,r longitudinally through the casing is a helically formed parti= tion it which provides a spiral pas passare through the casing. 'n dow ot gases entering the casing through. the inlet il be whirled rapidly 3o around the spiral path, and as they progress therealong between the successive convolutiona oi the partition the lichter portions of the mixed gases will. concentrate in the central portion of v the casing while the heavlon gases under cene 35.

arating device, the number of convolutions of the partition therein, the velocity of :now of gases, i5

and to a certain extent the diameter of the casing which determines the width of the spiral path also constitute important factors in the results obtained. It is important to state, however, in this connection that in constructing the device 5o special precautions should be taken so thatthe walls of the casing and the helical partition should be smooth and without abrupt projections of corners such as might produce eddy currents or other agitation in theg'ases during their ow 55 through the separator or otherwise impair the separation treatment under centrifugal action.

As shown in the drawing the gas inlet II projects at an angle to the longitudinal axis of the casing so that the ow of gases immediately begins to spiral as it enters the casing and enter upon its spiral course therethrough without unnecessary agitation.

The particular form of the invention illustrated is intended todiv-ide the gases into two concentric zones. Separate outlets are provided for the removal or discharge of the gases from each zone. For the removal of gases from the outer zone adjacent the periphery of the casing, the tubular casing wall is provided with a series -of fairly smallspaced apertures I3. Such apertures will-be arranged around the circumference of the wall and may comprehend a longitudinal area thereof' in the region of the outlet end of the spiral gas passage-of a proportion dependent upon the rapidity with which the heavier components of the gases to be treated will be forced out to the periphery of the casing. It will be understood, of course, that the arrangement of the apertures will be such as to conform to the convolutions of the passageway.

It is deemed desirable to surround the apertured portion of the casing II with an encompassing jacket or outer casing Il which with the wall of the main casingA defines an annular chamber I5. The heavier gases discharged from the spiral passageway through the apertures I3 are collected in the chamber I5 The outer casing is preferably closed at its ends .and provided with a single outlet port or pipe I6 at one end through which the heavier gases may be Withdrawn as rapidly as they pass out ofthe main casing I0.` l

The withdrawal of the lighter separated gases from the central portion of the casing is effected through-a pipe I'Ir which extends longitudinally of the casing at thel center thereof. To this end the helical partition I2 is formed to provide av central opening for the receipt of such pipe. The inner edge of the bafile will be supported by and secured to `said pipe as well as by the tubular wall of the main casing. By this arrangement the vgases in their spiral course will pass around the pipe in contact therewith, and under the separatingaction the lighter gases will form into a centralzone which may be withdrawn through the pipe.

Apertures 2| which may be similar to the casing apertures I3. are provided in the pipe I1 through which the gases from the lighter central zone are withdrawn into the pipe and carriedl away. Such apertures may occupy the same longitudinal area of the casing as the outlet apertures for the heavy gases in the periphery of the casing. Since the separation of the gases becomes more complete as they progress through the casing, the apertured portion of the pipe I1 should traverse at least the final portion of the spiral path. In the embodiment of Figure 1, the pipe I1 is shown as traversing the full length of .the casing and having an outlet end I8 extending out through the inlet end of the casing. In such arrangement the other end I9 will be closed. A

With the 4apertured pipe I8 for withdrawing the lighter gases frointhe central zone and the apertured peripheral area of thel casing for Withdrawing the heavier gases, a solid wall 20 may be provided at what would normally be the outlet endof the casing. l

of the pipe I'I ous longitudinal points.

The higher the velocity of ow of gases through a separator such as just described, the greater the centrifugal force and the more complete the separation. It ls therefore deemed important that the velocity of flow should not diminish as the gases progress along their spiral path through the separator. Since, as above stated, it is contemplated to withdraw gases at various longitudinal portions of the central pipe and the separator casing, there might be some tendency for the velocity to diminish because of the reduction in volume of the gas'es from such withdrawals. To overcome this possible difilculty, the modified construction shown in Figure 3 may be employed. The particular feature of such arrangement is that the spiral partition generally denoted Aby the numeral is so formed that the pitch and spacing of its successive convolutions progressively diminishes in the direction of the outlet end of the separator. Thus, it will be noted that the convolutions 26 and 21 at the inlet end of the casing are fairly widely spaced, while at the outlet end the convolutions 28 and 23 are fairly close together. In this manner the cross-sectional area of the spiral passage formed by the successive convolutions of the partition 25 progressively diminishes so that as the volume of the gases flowing is decreased by Withdrawal at progressive longitudinal points by the apertured casing portion 30 and the central pipe 3|, the decreased volume of gases still ilows with the same velocity. A further modified construction is shown in Figure 4. Here the tubular casing 32, instead of maintaining a constant diameter throughout its length, progressively inpreviously described embodiments the casing wall Will have an apertured area 33 in a portion thereof, removed from the gas inlet 34, through which the heavier separated portions of the gaseswill be withdrawn. casing 35 is to be provided in the apertured area, it Will also assume a conical form and at its end gradually decrease in cross-section to provide a smooth Walled area terminating in an outlet 36. Ii' desired, the end Wall 31 of the main casing 32 may be of conical shape to complement the end wall 38 of the outer casing and form therewith a'conical passage to the outlet 36 of gradually increasing area.

As in the previous embodiments a central pipe 39 Will extend through the casing for the Withdrawal of the lighter gases, the same being apertured at various longitudinal portions in the region of the outlet end of the casing 32.

The helically formed partition plate 40 will gradually increase in diameter to conform to the increasing diameter of the casing 32. Since with the progressive increase in diameter of the casing the diameter of the spiral passage also various points of its length will have substantially the samecross-sectional area despite the progressively increased diameter thereof'.` In the embodiment of Figure 3, progressive diminishment in the spacing of successive convolutions of the partition was intended solely to compensate for the portions of gases withdrawn at vari- In the embodiment of Figure 4, therefore, where the diameter of the casing increases, the progressive decrease in spac- If an outer.

separation aumen lng of the successive convolutions of the partition must be more abrupt.

An important advantage in the conicallarrangement of Figure 4 is that while the velocity of the gases at the inner part of the spira-l path. does not increase as long as the diameter of the central outlet pipe for thelight gases does not change, the velocity of the gases at the outer peripheral portion of thepath increases with the 'increase in diameter of the casing. That is to say, the velocity differential betweenthe flow at the outer and inner portions of the spiral-path becomes greater. This of course induces a better between the lighter and heavier gases. Such effect will be controlled by, the width of the spiral path in relation to-,the diameter `of the casing as determined by 'the spacing of the convolutions of the helical partition.'

The embodiment shown `in Figure 5 is some-V what similar to that of Figure 1, but'is simpler and at thev same time calculated to produce more efficient separation. The casing 4| is provided with a gas inlet pipe, orport 42, at the inlet end which opens into a spiralpassa'geway defined by the helical partition 43 wound about the central core 44. It Willbe noted that the spiral passageway contains a greater number ofcon- I volutions than the constructionV of Figure 1. Within practical limits -the longer the passageway the more prolonged will be the centrifuglng action and the more Vefiicient the operation of the device .in separating the exhaust gases. It will further be noted that the radial -depthof the passageway convolutions has been substantially increased as compared with 4the constructionin Figure 1 by increasing the diameter of the casing 4i in relation tothe diameter of the core 44.l It will be understood that the deeper the cross-section of the convolutions the greater will be the velocity differential of the gases between the inner portion and the peripheral area thereof. It will also be `noted that the passageway convolutions are relatively narrow in cornparison with their radial depth. .Such proportioning of the cross-section' of the convolutions is calculated to be incre conducive to the stratirlcation of the'lighter gases in the core area and the heavier gases in the peripheral area ofthe passageway.

The withdraws. of the lighter portions of the centrifuged gases will be made at the core areaof the passageway,.and as before the conduit means for withdrawing the lighter gases will preferablyloe accomplished by forming the core, or at least a portion of the'length thereof., as a hollow pipe having an outlet 45 extending out of the casing and adapted to supply gases unmixed with the gases collecting in the peripheral area oi the passageway,

Instead of discharging the remainder of the gases from the passageway through a series of ports in the periphery of the casing, the gas outlet means at the outlet end 'of the casing takes the iorm of an outlet port 416 located in the end wall tl. This dispenses with the necessity of the peripheral ports it .as shown in-f Figure l, and also eliminates the utility of the outer Ajaclret it. l

The port @it will be of sumcient 4size as to rapidly and continuously discharge gases from the passageway so that a high velocity of flow 'may be maintained through the casing. If desired the entire end wail 41 may be dispensed with so that the gases will discharge directly into the atmosphere from the end of the passageway as defined by the helical partition 43.

The gases from the inner area of the passageway are collected into the conduit 48 embodied in the core 44 through a series of ports 49. The size and number of ports 49 may require some experimentation in order that for a given internal combustionengine the vcomposition and volume cf the gases withdrawn will produce most emcient results. With a construction such as in Figure 5 it may be desirable as shown to diswlth ports 49 at the last few convolutions of the passageway, and also to provide a closed end 50 for the conduit in order ,to make sure that heavier portions of the gases centrifuged into the peripheral area of the passageway and which are about to discharge through the port 48 will not inadvertently'pass into the conduit 48.

The cross-sectional area of the convolutions of the passageway will be approximately of the same order of size as the inlet port 42. The port 42 is assumed tovbe of approximately the same diameter as internal combustion engine. Desirably the crosssectional area of the passageway may be made somewhat smaller in order that the gases assume an increased velocity'in vthe passageway over their speed in the exhaust pipe. As previously explained the higher the velocity f the gases through the passageway the greater the centrifugal action and the more complete the separation.

The embodiment of Figure 5 represents a construction of the invention particularly adapted for operation with ay popular make six-cylinder automobile engine. The tubular casing has an inside diameter of six inches and the central core 44 has an outside diameter of one and onefourth inches with a `one inch bore. The inlet port has a diameter of approximately one and one-half inches. There are twenty-one convolutions of the helical partition with a spacing be- I the exhaust pipe from the termination of the tween successive convolutions of about threefourths or seven-eighths of an inch.

in addition to centrifugally separating the exhaust gases discharged from an internal combustion engine the present invention, by reason of the spiral construction" of the partition in the casing, serves to baille the gases and functions as a mufiier. When employing the invention the usual type of muffler is entirely dispensed with.

rlihe present application is a continuation in part of my present copending and allowed application `Serial No.722,601, :lled April 26, i934. The invention herein described is particularly 'applicable to the treatment of exhaust gases of internal combustion engines, as for example under the process and system disclosed and claimed.4 in my copending application Serial No. 722,600,`

hled April 26, 1934.`

it is evident, of course, that'the idea of separating mixed gases centrifugally into concentric strata' `-and removing. the gases independently from such strata may-loe carried out by modifying the device herein specifically shown and desribed'without departing from the scope of the invention as set forth in the accompanying claims.

l claim:l A

l. A combustion gas refining device for centrifugally, treating a flowing "stream of the mixed combustible and incornbustible gases generated byv the combustion of fuel, andl adapted to recover thereirom a refined combustiblegas supply for recombustion containing an increased proportion of the lighter combustible gas constitu- `ents and a decreased proportion of the heavier incombustible `gas constituents of the original mixture, said device including a closed helical conduit having radially deep convolutions in which the stream of combustion gases is centrifuged during passage therethrough. a gas inlet port for the admission of the combustion gases opening into one end of the spiral conduit, a

i gas inlet apertures in the pipe opening at the inner periphery of the conduit convolutions through which the centrifuged lighter portions of the mixed gases are withdrawn into the pipe, an outlet 'end on the pipe opening outside the conduit adapted to be connected with a gas supply line and through which the lighter centrifuged gas portions discharged from the conduit are withdrawn, and an independent waste gas second outlet means in the conduit for discharging from the conduit the residual centrifuged heavier portions of the mixed combustion gases.

2. An internal combustion engine exhaust pipe attachment for cntrifuging the flow of exhaust gases discharging from an -engine and developing from the gases a portion of improved composition fo'r combustion purposes, comprising a helical centrifuging conduit of relatively large outer diameter and having radially deep convolutions adapted to cause gases froman engine exhaust pipe to iiow therethrough at high velocity in the form of a radially thick st eam, anexhaust pipe connecting-fitting at one\\end of the conduit adapted to discharge into the conduit the stream of gases from the exhaust pipe, a central pipe closed to the admission of air around which the convolutions of the helical conduit extend l. communicating with only the inner periphery 'of convolutions of the conduit, said pipe being adapted to withdraw centrifuged gases from the inner periphery of progressive convolutions of the conduit, and waste gas outlet means adapted to discharge from the conduit in a continuous stream the remaining centrifuged gases.

3. An exhaust gas separating device for centrifugally developing from internal combustion engine exhaust gases a gas supply of combustibly improved4 composition suitable for re-use in an engine, comprising a tubular casing, a gas inlet port at one end of the casing, a radially wide helical partition extending through thecasing around the central core area. thereof and definlng between the casing and said central core area a deep continuous spiral passageway through which gases will be caused to flow at highvelocity in the form of a radially thick stream, a discharge port in the casing opening to the atmosphere providing for a continuous high velocity ilow of gases through the passageway and a continuous high velocity discharge of centrifugedl gases from the passageway, and a gas conduit joffrelatively small diameter extending through thecential core area of the casing and forming' 'the inner wall oi' the spiral passageway and.

adapted to withdraw centrifuged gasesfrom the inner periphery lof the passageway, said gas con- Lduitbeing closed to the admission of gases discharged i'rom the outer peripheral area of the passageway and also being closed tothe admission of air from without the casing.

4. An internal combustion engine exhaust pipe attachment for centrifuging the flow of exhaust gases discharging from an engine and developing therefrom a portion of combustibly improved composition forrecombustion, comprising a tubular casing, a small central pipe extending through the casing and forming therewith a radially deep annular chamber, a partition wound about the central pipeLand forming said chamber into a closed spiral gas passageway, a gas inlet port at one end of the casingdischarging into the gas passageway, gas inlet means in the central pipe communicating only with the spiral gas passageway and comprising inlet apertures opening at the inner periphery of the passageway for withdrawing lighter centrifuged portions of the exhaust gases, and an independent waste gas outlet port in the casing for discharging the residual heavier centrifuged gases from the spiral passageway.

5. An exhaust gas separating device for centrifugally developing from internal combustion engine exhaust gases a gas supply of improved composition fo'r reuse in an engine, comprising a tubular casing having therein a continuous helical partition surrounding the central area of the casing and defining a helical passageway of greater radial depth than width lthroughout its length, an inlet port in one e'nd of the casing communicating with the inlet end of the passageway, a conduit leading'outI of the casing communicating with only the inner portions oi convolutions of the passageway immediately -surrounding the central area and adapted to withdraw gases from the passageway for reuse in a continuous stream and unmixed with other gases, and a gas. discharge \outlet in the casing propassagewayvof the remainder of the gases.

6. An exhaust gas separating device for centrifugally developing from internal combustion engine exhaust" gases a gas supply of improved composition for reuse Ain an engine, comprising ing through the casing around the central area thereof, the convolutions of said partition extending perpendicular to the axis of the casing and forming a continuous helical passageway of substantial radial depth, a pipe in the central' area of the casing closedf to theadmission of air and having ports therein directly communicating with lthe inner area of convolutions of the passageway adapted to withdraw a portion of the gases from the passageway, independent;

composition suitable for vreuse in an engine, comprising a tubular` casing of relatively large diameter having formed therein and extending therethrough a continuous helical passageway,

said passageway being constituted as a multi- ,70h

plicity of closely wound helical convolutions of a tubular casing, a. helical partitionm extend- 45 substantial radial depth to permit space for strat'- ilcation of the lighter and heavier gaseous components of the Aexhaust flow under centrifugal action, a gas inlet adapted to be connected to" -casing of relativelylarge diameter, aA gas inlet an engine exhaust line located at one end f the casing and opening into 'the inlet end of the passageway, thegas inlet and cross-section of4 the passageway convolutions being of the same relative area and adapted to cause the exhaust to flow through the casing under the high ow velocity with which it discharges through an engine exhaust line, said passageway being entlrely closed to escape of gases for a substantial distance lengthwise of the casing from the* inlet end to provide for a confined flow through anumber of convolutions rof the passageway of the entire volume of exhaust gases entering the casing inlet, a gas discharge outlet atthe other end of the casing communicating with the peripheral area of the passageway and permitting `a high velocity discharge of gases from the casing, and an independent second gas outlet means comprising a pipe of substantially smaller diameter than the' casing extending centrally' of the casing having gas intake openings thereinlocated beyond the entirely closed portion of lthe passag'eway and communicating with the inner area of the passageway convolutions-adjacent the cutletend of the casing, said pipe being closedto lthe admission therein of air fromwithout the casing and having an outlet end extendingout of the casing and adapted to be connected with a gas supply line.

8. An exhaust gas separating device-for centrifugally developing from internal combustionv engine exhaust gases a gas supply of improved composition suitable for reuse in an engine, comprising a tubular casing having formed therein a continuous helical passageway constituted. as

a multiplicity of convolutions which are closely wound and of such radial depth as to provide space for the formation of relatively thickgas strata therein under centrifugal force, said passageway including a closedv initial centrifuging outer area of said subsequent portion ofthe passageway and permitting a `high velocity flow of gases throughthe casing, and a second gas outlet comprising a gas collecting pipe of substantially lsmaller diameter than the casing located centrally of the casing, said collecting pipe being closed to the admission therein of gases from without the casing and havingv -intake openings communicating only with the inner area ofthe convolutions of the subsequent passageway portion adjacent the outlet end of the casing and said pipe being'closed to direct communication with the passageway convolutions of the initial centrifuging portion, said pipe extending out of the casing and having an outlet` end portion adapted to be connected with a gas supply line to an engine.

9. Anl exhaust gas separating device for use" for. use in an engine, and comprising a tubular port of substantially less size than the diameter of the casing located at one end of the casing and. adapted to be connected to the engine exhaust line, a waste gas' discharge outlet at the other Vend of the casing adapted to discharge gases from the peripheral larea of the passage to the atmosphere and permitting a high velocity flow of gases through the casing, a second gas outlet fori-'withdrawing gases from the casing for engine use comprisinga pipe of substantially smaller diameter than the casing located centrally of the casing andhaving an outlet end extending outv of the casing throughl which gases separated from the discharge through the waste gas outlet can besupplied for engine use, a helivcal partition extending through the casing around the Icentral, pipe comprising a multiplicity of closely wound convolutions forming with the central pipe and casing periphery a helical passage -of substantial radial depth and having a crossse'ctional area of the same order of size as the casing inlet, s aid pipe being closed to direct communication with the casing inlet and with the convolutions of the passage for a portion of the length of the casing adjacent the inlet so that gases can not enter the pipe until they have been centrifuged, said pipe being closed to the admission of air from without thecasing and having intake openings communicating with` the con'- volutions of the passage adjacent the outlet end of the casing for withdrawing lighter centriiuged portions of the exhaust gases which concentrate in the inner areaofthe passageway.

l0. A centrifugal gas separator for treating internal combustion engine exhaustgases comprising a tubular casing, a heiically formed partition defining a spiral gas passage through the casing, a gas inlet at one end of the casing, a discharge outlet, a pipe closed at one. end and having anoutlet end leading o ut of the casing for withdrawing gases therefrom and extending centrally through the .helical partition, said pipe defining the innerwall of the spiral gas passage formed Vby the partition'and having apertures at successive longitudinalY points for the removal of gases fromthe central portion of the spiral passage, the convolutions of the partition progressively becoming more closely spaced and defining a gradually narrowing gas passage from the inlet to the far end of the casing so as to4 avoid reduction in velocity of the spiral flow of gases as the volume of the gases is diminished by withdrawal through the apertures at the successive points longitudinally oi thel central pipe.

l1. A centrifugal gas separator for treating internal combustion engine exhaust gases comprising a tubular casing, an inlet at one endsof the casing,- a helically formed partition extending through the casing and deiining therein a spiral gas passage, a solid Wall at the other end of the casing, gas discharge apertures at succesive longitudinal points of the side wall of the casing for removing gases from the outer -portion of the spiral passage, a centrally located pipe around which the helical lpartition is wound having one endl closed and having its other end leading out of the casing, said 4pipe having gas inlet apertures at successive longitudinal points for the removal of gases from the inner central portion of the spiral passage formed by the partition, the convolutions of the partition being widely spaced at' theinlet end of the casing and progressively becoming more closely spaced to define a.` gradually narrowing passage `so as to avoidreduction in velocity o! the spiral ilow of gases as the volume of the gases diminishes with withdrawals at the inner and outer portions of the passage through the central apertured pipe and casing side wall.

12. A centrifugal separator for treating internal combustion engine exhaust gases compris-v ingfatubular casing, a gas inlet at one end of- 'the casing,- an apertured central pipe extending through the casing for withdrawing gases therefrom, further gas outlet means for .discharging from the casing gases other than those withdrawn lthrough the apertured pipe, a hellcally formed ternal combustion engine exhaust gases comprising a conical casing having a spiral gas passage therethrough, 4a gas inlet at the smaller end of the casing communicating with the corresponding end of said spiral gas passage, the inner periphery of the successive convolutions of said 4spiral passage being4 ofA constant diameter throughout the casing and the outer periphery of the spiral passage progressively increasing in diameter from the inlet end with the increase in diameter oi.' the conical casing, whereby to produce an increasing diierential at progressive portions of the casing between the flow velocity of the gases at the outer and inner peripheries of the spiral passage which is conducive to. better separation of the heavier from the lighter gases, the width of successive convolutions of the spiral passage decreasing progressively from the inlet end o! the casing as the diameter of the passage increases, and separate gas outlets in the casing fordischarging centrifugal gases from the outer and inner peripheral portions of the spiral gas passage.

GEORGE L. PRATT. 

